A general question about gravity

I remember reading something similar to this somewhere but now I can't remember. Is it true that eventually gravity fails and the planets will fall out of their orbit and collide...or something like that? I find that kind of hard to believe because for that to happen wouldn't it mean that we would need the energy to be zero and that's highly unlikely to happen? Anyways, thanks in advance. Oh and if anybody knows of any credible websites that have to do with this, please do post them. Thanks